Packaging materials of paper and board have been used for a long time for packaging of different goods so as to provide mechanical and/or chemical protection for the goods. For example perishable products, such as food products, healthcare products and electronic devices have been packaged in paper or board packages provided with a barrier that provides protection against chemical influence, e.g. against gas, such as oxygen, liquid, aroma, oil and/or grease. Packages function in a two-way manner, which means that liquid from the inside of the package is prevented to leak out and the liquid outside the package is prevented to leak inside the package. The same applies for oxygen, aromas, oil and grease.
It is important that the packaging materials can provide an oxygen barrier especially in case of perishable products that are sensitive to oxygen since bacteria are aerobic and thus need oxygen to grow. Therefore, a barrier against oxygen is needed to provide extended shelf life for the packaged product. Oxygen barriers can be provided for example in the form of various polymer coatings, such as ethylene vinyl alcohol (EVOH), ethylene vinyl acetate (EVA), nylon MXD6, polyvinylidene chloride (PVDC) and liquid-crystal polymers (LCPs) coatings. The coatings may be applied on a substrate for example by means of extrusion coating or as e.g. an aluminium foil. A drawback with extrusion coating is, however, that it is difficult to combine in existing production lines for paper and/or board materials in an efficient way, since in connection with extrusion the substrate needs first to be dried, then coated and then dried again. Such production lines are not energy efficient. Thus, there is a need to be able to combine or integrate a coating process to the existing paper or board production lines in an energy efficient way. Other possibility to provide a barrier is to apply a layer of aluminium foil to the substrate. Aluminium provides an excellent barrier but increases the carbon dioxide load (carbon foot print) of the product and also makes the product difficult to recycle.
In view of the prior art, it is desirable to at least partially replace existing coating processes and coating materials with more energy effective and environmentally friendly processes and coating materials. The packaging material should also be easily recyclable and/or biodegradable to decrease the environmental load and carbon foot print.
WO2011056130 discloses a process for producing a coated substrate comprising cellulosic fibres by applying a dispersion coating composition comprising MFC (microfibrillated cellulose) in an amount of 0.5 to 20 weight-% and colloidal particles of a polymer which can be polyvinylidene chloride (PVDC), polyvinylalcohol (PVOH), ethylene vinyl alcohol (EVOH), acrylate copolymers, modified styrene, butadiene, polyolefins, acrylonitrile, fumaric and maleic diesters, cellulose esters, starch ethers, different acrylates or methacrylates, vinyl acetates, polymers which origins from potato, corn, cereals, wood, xylane or similar products or a composition of any of these polymers on the surface of the substrate. The coating provides a barrier. However, the disclosed composition comprises a major amount of colloidal particles of a polymer, and as mentioned above, it would be desirable to replace at least partially such coating materials. Also, it has been mentioned that the coating can be performed on-line or off-line, but it has not been disclosed how the production can be performed on-line or off-line.
WO2013027103 discloses a process for providing a substrate with a barrier comprising coating the substrate with a coating composition comprising at least one water soluble polymer, such as PVOH, carboxymethyl cellulose (CMC) and/or hemicelluloses, and a nano-particle being a nanoclay, MFC, aluminium silicate, nano precipitated calcium carbonate, nanotalcum, nanotitanium dioxide, xylene, carboxy methyl cellulose and/or silica. The composition is coated on the substrate by means of foam coating, blade coating or by means of a size press. The coated substrate is then dried and an aqueous barrier activating solution is added to the substrate. However, there is no mention that this coating process can be integrated in an easy way to existing production lines for paper and/or board materials. Also, since the coated substrate needs to be activated after drying, an additional drying and activation section in the paper machine is required.
Thus, even though there are prior art solutions for coating processes there is still a need to improve the integration of a coating operation into a paper making process in a simple and energy efficient way. There is also a need to combine or integrate a coating process into existing paper or board production lines. Further, there is a need for an environmentally friendly process to provide a coating functioning as a barrier for a substrate. There is also a need for an environmentally friendly packaging material which is easily recyclable while it comprises a high quality barrier.